Cessna 150 accident near San Juan, Puerto Rico, June 1, 2024

The NTSB's narrative final · quoted from the NTSB record

The student pilot and flight instructor reported that the engine lost power shortly after takeoff. ADS-B data showed that the airplane reached a maximum altitude of 213 ft above ground level (agl) before entering a descending left turn back toward the runway. The airplane impacted the ground before reaching airport property. Examination of the wreckage found substantial damage to the engine mounts, fuselage, both wings, the right horizontal stabilizer, and elevator. Examination of the engine revealed that the rocker shaft bosses for the No. 2 cylinder had failed. Metallurgical examination found that a portion of the cylinder head, which contained the rocker arm shaft, fractured due to fatigue cracking that had initiated along the bore for the shaft. Once this section of the cylinder head fractured, the remainder of the cylinder head holding the rocker shaft fractured from overstress, freeing the shaft and rocker arms. These fractures would prevent the proper function of the drivetrain, preventing the valves from opening and leading to the failure of the No. 2 cylinder. The housing boss bore walls exhibited wear significant enough to allow for movement of the bushings and shaft. The bore exhibited wear marks consistent with rotational and lateral movement of the shaft, and the adjacent bushings exhibited lateral wear marks. Many of these marks matched those observed on the shaft, indicating movement along these surfaces. This uneven wear likely led to the rocker arms pushing erratically on the valves, as evidenced by the off-center wear marks on the rocker arm and valve stem faces. This uneven movement and wear likely led to wobbling and sliding. This created more wear, which eventually resulted in fatigue cracking and the subsequent failure of the rocker shaft bosses. A review of maintenance records was unable to determine the number of hours on the cylinder. The review found no record of the No. 2 cylinder being removed and reinstalled on the engine. While the logs described that about 7 years before the accident three unspecified cylinders had been removed and replaced, no information regarding which position they were installed to, or their serial numbers were recorded. The engine was subject to an FAA airworthiness directive (AD), which stated that the cylinder rocker shaft bosses must be inspected “At the next cylinder removal from the engine, or engine overhaul, whichever occurs first, after the effective date of this AD, inspect the cylinder rocker shaft bosses for cracks….” Based on the records, it could not be determined whether the No. 2 cylinder had been inspected in accordance with the AD.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.

Photographs from the investigation 6 pictures from the NTSB's docket, as the NTSB released them

Photograph 1 – Airplane at the accident site.Photograph 3 – View of the tail and right wing of the airplane.Photograph 4 – View of the engine prior to teardown.Photograph 5 – View of the No. 2 cylinder rocker box cover with fractured parts.Photograph 6 – View of the No. 2 Cylinder with rocker box cover removed.

The NTSB's photographs with the NTSB's captions, at screen size. Open a picture to see it full size or to report one that should not be shown.